1. Field of the Invention
The present invention relates to a cardboard type liquid packing container and, more particularly, to a bottom structure of the above-mentioned type liquid packing container in which square or rectangular recessed portions are formed at the inner central portion of the bottom thereof and the ends of the cardboard are uniformly bonded to each other, so that liquid leakage is prevented. In addition, since the corner portions of the bottom of the container are trebly folded, the container is so tough that leakage from the corners is prevented. Further, the container enables economical use of cardboard.
2. Description of the Prior Art
Recently, among containers for various materials, a cardboard type container fabricated by folding a relatively thick cardboard has been widely used to pack liquids. Such a container has been used that its value as a commodity is enhanced by printing various patterns etc. on its surface because it is relatively tough; that it is easily transportable, storable or the like because it can be formed into an accurately triangular shape; that it is easily disposable without generating a pollutant after use; that its humidity resisting property is improved if a thermoplastic synthetic resin is laminated on the surface thereof; and that its sealing property is excellent without using any special adhesives.
As a result, with respect to the cardboard type liquid packing container having such various attributes, a thicker cardboard has been increasingly used during recent years due to an increase in amount of the liquid contained therein. For this reason, it is necessary that the number of cardboard laminations in the bottom surface of the container be reduced to enhance the upright stability thereof; that any gaps be eliminated from the cardboard laminated and bonded together in constructing the bottom surface, thereby improving the sealing property; that, especially in view of using this container so as to accommodate liquids, an unreasonable force not be applied to the corner portions thereof; that mass production thereof be possible; and that the amount of cardboard used for each container be reduced.
As one example of the milk containers widely utilized during recent years, Japanese Utility Model Publication No. 46-4661 discloses a bottom structure of the liquid packing container as shown in the expansion plan view of FIG. 1. The most characteristic feature of this bottom structure lies in that the portions of the free edges of the cardboard which are in contact with the liquid charged in closing the bottom portion is minimized, and the panels 10, 11 to be folded inwardly of the container have an isosceles trangular shape wherein a vertical angle is less than 90.degree., rather than a right-angled isosceles triangular shape, so that the respective free edges X, X' and Y, Y' of the triangular panels 10a and 10b, and 11a and 11b to be folded firmly engage each other.
Applicant has conducted various investigations with respect to conventional cardboard type liquid packing containers and found that, in such a liquid packing container as disclosed in Japanese Utility Model Publication No. 46-4661, since the panels 10, 11 to be folded have a triangular shape, namely, their apex portions converged on a point, when the triangular panels 10a, 10b, 11a, 11b are folded along the folding lines at the both sides of the panels 10, 11, it is difficult to fold the triangular panels 10a, 10b and 11a, 11b in the vicinity of the apex portions of the triangular panels 10, 11; and when a flat bottom is formed by forming the panels 10, 11 into an acute-angled isosceles triangular shape and by folding the triangular panels 10a, 10b, 11a, 11b, the respective free edges X, X' and Y, Y' of the folding panels 10a, 10b, 11a, 11b are engaged with each other such that a strong force is applied to the central portion of the container to produce gaps in the side of the peripheral portion of the container, whereby the liquid packed therein is apt to leak.